Extremely sensitive low cost acoustic sensors are required for a wide range of applications, many of which involve operation under hostile environments. A typical example is a geophone used to record the response of the earth to acoustic impulses applied thereto in the search for minerals and petroleum both on land and under water. It has been recognized that fiber optics may allow the construction of rugged high performance microphones. In particular, approaches have been developed successfully which are based on the comparison of light passed through a reference optical fiber shielded from acoustic noise with light passed through a second sensor fiber which is subjected to the acoustic energy wished to be detected. One such approach is reported in U.S. Pat. No. 4,297,887 entitled "High-Sensitivity, Low-Noise, Remote Optical Fiber" by J. A. Bucaro. Unfortunately, such devices are not always able to provide features and desirable attributes such as automatic noise suppression, low cost, small size, simple design, and ease of incorporation in acoustic sensor arrays. These and other more sensitive devices, such as taught by Cahill and Udd in U.S. patent application Ser. No. 225,731, require electronic feedback mechanisms for readout and signal stabilization.